CASTLE ROCK — The PGA Tour’s best hunter arrived at the driving range Thursday at 8:30 a.m. Two golfers to his right, the guy everyone else is chasing, was already into his pre-round routine ahead of their 9 a.m. tee time. The two best golfers in the world were paired together in the first round of the BMW Championship at Castle Pines Golf Club, and a large throng of patrons followed their every move around the 8,130-yard course. It has been a spectacular year for Xander Schauffele, including two major championship victories.